Quantum teleportation achieved over ten miles of free space

Scientists have recently had success teleporting information between photons …

Quantum teleportation has achieved a new milestone or, should we say, a new ten-milestone: scientists have recently had success teleporting information between photons over a free space distance of nearly ten miles, an unprecedented length. The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal, and that the ten miles they have reached could span the distance between the surface of the earth and space.

As we've explained before, "quantum teleportation" is quite different from how many people imagine teleportation to work. Rather than picking one thing up and placing it somewhere else, quantum teleportation involves entangling two things, like photons or ions, so their states are dependent on one another and each can be affected by the measurement of the other's state.

When one of the items is sent a distance away, entanglement ensures that changing the state of one causes the other to change as well, allowing the teleportation of quantum information, if not matter. However, the distance particles can be from each other has been limited so far to a number of meters.

Teleportation over distances of a few hundred meters has previously only been accomplished with the photons traveling in fiber channels to help preserve their state. In this particular experiment, researchers maximally entangled two photons using both spatial and polarization modes and sent the one with higher energy through a ten-mile-long free space channel. They found that the distant photon was still able to respond to changes in state of the photon they held onto even at this unprecedented distance.

However, the long-distance teleportation of a photon is only a small step towards developing applications for the procedure. While photons are good at transmitting information, they are not as good as ions at allowing manipulation, an advancement we'd need for encryption. Researchers were also able to maintain the fidelity of the long-distance teleportation at 89 percent— decent enough for information, but still dangerous for the whole-body human teleportation that we're all looking forward to.

The answer has always been abundantly clear, at least as far as I am concerned. It is through the vehicle of sensational Press Releases, full of layman's buzzwords and layman's hypotheses, that companies are able to convince venture capitalists, government entities, and other such financial organs to part with their cash so that said technology company can stay in business and feed its employees and write new & improved press releases further on down the line that imply all kinds of fantastical technologies without ever actually promising anything.

There are various groups of greedy pinheads around the world that are constantly looking for "exciting new investment possibilities" so that they can invest "on the ground floor" and reap staggeringly fat wallets when the "promised" (never actually promised but always implied) technologies come to market. Buzzwords like "teleportation" and "nanotechnology" and "FTL travel" and so on are typical of these kinds of specious press releases, because, after all, everybody knows that all you need to do to understand these concepts is to watch Star Trek, right? Rii-i-i-i-i-ight.

You can bet that whenever these investors read the word "teleportation" their first thought is, "Beam me up, Scotty!" which is quickly followed by their second thought, which is: "I'll be richer than I can imagine when this thing comes to market, so I need to invest a little today to reap the bonanza tomorrow!" As these companies still exist and are still writing such press releases, there can be no doubt that this strategy has been successful for them in raising enough money to pay themselves handsomely.

As well, although the words "quantum" and "teleportation" did not achieve their current generic, populist technological definitions as concepts until during the last 50 years or so, it's worth noting that prior to that the word "teleportation," for instance, had been primarily linked to the occult in one form or another. Too, we've had through the years various interest and funding by the government in ESP and precognition studies and other things that are so bizarre they've been papered over in the ensuing decades by reams of bureaucratic wallpaper.

There's also another, more cynical, reason for these kinds of fantastic press releases which imply so much and promise so little, and that is "misinformation." Governments often use such vehicles to deliberately misinform other governments about their technological prowess so as to create the specter of doubt, if possible, in the minds of possible enemies. It is widely speculated today that much of the post WWII UFO propaganda generated by the government--with Roswell being a prime example--was done specifically to confuse and confound nations like the USSR, which in the latter 1940's and later were considered high risks in terms of their willingness to ignite a nuclear war. This is the kind of strategy that once initiated by a government is never revealed officially to be the actual SCAM that it was, etc.

I guess the bottom line is that until we see "Brundlefly" or "Beam me up, Scotty!" demonstrated in the form of workable and viable technologies that can actually be marketed by a company--we should take all of these other technological implications about the immediate or near-term viability of such technologies with an enormous grain of salt.

I'm an idiot, so... I really don't understand the difference between that and this: taking two balls, one white, and one black, and placing them randomly into two identical boxes. I give one box to my friend who drives 3000 km across the country, at which point I open my box and *instantly* know the information contained in his.

Putting aside the question of information transfer a moment, let me address why the quantum situation is different from your white ball/black ball example. In the classical world you say "Yes - a ball must be black or white." But in the quantum world you can really be the superposition between black and white. It's NOT as if it's really one or the other but you just don't know. It's literally both at the same time.

You can "entangle" two "balls" such that if you measure one ball to be black, you know the other has to be white - probably due to some conservation law. The teleportation/spookiness part comes in when you then separate the two balls (here by 10 miles) and measure one, then the other and find they are consistent (one white, one black). In the classical world this makes perfect sense as your example demonstrates. But in the quantum world, both balls were in a half white/half black superposition. And somehow when you measure one, the other instantaneously "knows" which color it should be!

One is tempted to say, "This is dumb, it really was either white or black I just didn't have the correct theory to know which" This is called a hidden variable theory and has been shown to be false with great certainty:

Reading the first couple of comments, it's interesting to note that even if the "transmit information" phrasing in the article was an attempt to dumb things down for a wider audience, it's causing nothing but confusion. This perhaps demonstrates the intelligence of your audience and I would encourage you folks not to take after Wired but stick to your intelligent articles, intelligent audience roots.

Ignorance <> lack of intelligence.

I agree that the phrasing was misleading, but how would you have phrased it differently and still appealed to as wide an audience as possible?

Or: explain why you think science articles should only try to inform already-knowlegeable people, instead of also informing and educating laypeople.

I don't think that. Ars usually does very well making their articles approachable *and* accurate/informative to laypeople. Unfortunately, many people will come away from this with absolutely the wrong impression of what is happening.

Good point on ignorance vs intelligence though, I myself was guilty of bad phrasing there.

I learned ..... 1. Exciting and cool research is happening in this field and if I want to know more I can go look for it . 2. Transmission is a provocative word 3. Causality makes people nervous ( or at least violating it ) 4. nkinnan is a douche ( not my words )

Yes, nkinnan is being a real dick (seriously man- you offered nothing up to clarify the point, just bitched about what was there, and then insulted the rest of the audience. Classy. BTW-I know many things you don't-but hoarding and sticking up my nose wouldn't even occur to me- explaining and clarifying would) but there is a kernel of useful info there.

I did clarify, in comment number four: "No information is transmitted. The end state of the two photons is correlated but random."

That anger you feel towards me is very similar to the anger I felt when I realized how many people would walk away from the article thinking that we've figured out how to violate one of the most basic laws of the universe.

“Quantum Information” has nothing to do with information, by which I mean you cannot transmit (or teleport) a message of any kind using “Quantum Information.” Read the last paragraph of the article and tell me if that distinction is made clear to the audience, or even if the author demonstrates that they are aware of it. If your goal is to enlighten and educate your readers, and not simply make money off clicks, you’ve failed miserably.

And put me in the "disappointed with the insulters" column. We humans can't use our senses to intuitively understand quantum entanglement, unlike the way we understand velocity, acceleration, momentum, etc. So give us humans a chance to try to understand by rational thought -- of course, unless we're physicists we might fail, but give us a chance anyhow.

I've always been a bit skeptical of entanglement... with the main reason being that the quantum state is correlated, but we suspiciously lack any ability to influence anything with this connection (i.e. the no-communication theorem). For all intensive purposes, it really doesn't matter whether there is a hidden variable or whether there is some spooky wave collapsing action at a distance. You get the same result either way, and it doesn't help us at all.

I also do not really like how we casually dismiss the apparent violation of special relativity, just because the apparent faster than light transfer of information is of no use to us. The way I see it, you can't have it both ways. Either an entangled particle light years away really does instantly change the state of another particle/photon light years away (thus effecting the environment instantly, and implying a violation of relativity)... OR the outcome of any readings (Bell's inequality be damned) was decided ahead of time through unseen variables..

I think that a lot of the reaction stems from a natural defensiveness that people develop because they are so used to seeing science misrepresented on sites like slashdot. I, at least, tend to overreact because it depresses me to read all of the bizarre conclusions that people come to after reading and misunderstanding short articles on complicated topics.

I have to throw in that I think it's the scientists themselves which are misrepresenting the science. The word 'teleport' has a definition, and it's nothing like what is being achieved in these experiments. I understand that it's a complicated topic, but 'teleport' seems to be used because it makes for exciting paper titles rather than because it accurately communicates the ideas in the experiment.

If I understand the article, they sent photons from one location to another and using sophisticated measurements were able to determine that the photons arrived intact, unmolested, and probably unmeasured. The new aspect was the distance involved. But nothing about it resembled 'teleportation'. The media is just the messenger, the misrepresentation is coming from the source.

I love that white ball/black ball example, because it seems like a perfect analogy of quantum entanglement to me -- and thus reveals my low level of understanding of entanglement. I know at some level the ball analogy thing is incorrect, and of course the black and white balls are never entangled.

But still. If NO ONE knows what color the balls in the boxes are, then truly, opening the local box instantaneously determines the color of the distant ball. Like magic! Classical entanglement!

By the way, I do agree with others who believe we must tread carefully when talking about information transfer through quantum effects. Here, I think, would be the criterion for true instantaneous information transfer: Can one build a quantum walkie-talkie and transmit even one bit of actual information instantaneously over a distance? No? Then that's not true info transmission.

Yes, nkinnan is being a real dick (seriously man- you offered nothing up to clarify the point, just bitched about what was there, and then insulted the rest of the audience. Classy. BTW-I know many things you don't-but hoarding and sticking up my nose wouldn't even occur to me- explaining and clarifying would) but there is a kernel of useful info there.

I did clarify, in comment number four: "No information is transmitted. The end state of the two photons is correlated but random."

That anger you feel towards me is very similar to the anger I felt when I realized how many people would walk away from the article thinking that we've figured out how to violate one of the most basic laws of the universe.

We don't like to think of them as "laws", more like "guidelines", m'kay?

Seriously though, you have to be able to dangle a carrot to get people interested. The fifteen of you who read the front page and are well on your way to Complete and Sovereign Understanding of Quantum Mechanics should probably find your niggles with actual science publications. Not the guys who use the word "butt" in an article URL.

Regarding the white/black ball: my understanding of quantum physics is that a superposition acts differently than either individual outcome. Take the double slit experiment: a photon of light can take either the left or the right of two slits in a material. If you measure which slit the light goes through, you end up with two blobs of light at the far wall, from the paths where you saw it go through the left slit and the paths where you saw it go through the right slit. But if you don't measure, the light 'sort of' goes through both, acts like a wave and interferes with itself. So instead of two blobs you get alternating lines of light and dark. Each individual photon hits only one spot, but after enough experiments you see the shape emerge.

If you have your back to the slits, you could tell if they're being measured by looking at the pattern on the wall.

So my analogy would be to pretend the black ball weighs ten pounds and the white ball weighs twenty. If you put the box on a scale, you'd read 15: it's both the black and white ball. If you open the box, the weight turns into ten or twenty depending on what you see. Thus you could tell this isn't just a case of having a white or black ball, because then you'd have a definite weight reading.

Of course, this seems to communicate information...maybe someone more knowledgeable than me can explain where this breaks down?

No information is transmitted. The end state of the two photons is correlated but random. I'm disappointed that such a basic misunderstanding made its way into an article here. I'll ignore the last sentence as the second half of it was presumably a joke.

Thanks for clearing that up, because I was a bit confused myself. Mechanical engineer on this end.

There's a general feeling I get when I talk to laypersons that a great deal of people who are tangentially interested in physics believe that Quantum Teleportation is like basically waiting for some minor breakthrough to be come some sort of universal FTL communications device.

This is completely incorrect and is mainly based in them focussing on the word that's cool and and they get (teleportation) and basically equating the word quantum with the word magic, this is not their fault per-say as the popular science publications seem to be in no mind to dispel this myth.

There's a general feeling I get when I talk to laypersons that a great deal of people who are tangentially interested in physics believe that Quantum Teleportation is like basically waiting for some minor breakthrough to be come some sort of universal FTL communications device.

This is completely incorrect and is mainly based in them focussing on the word that's cool and and they get (teleportation) and basically equating the word quantum with the word magic, this is not their fault per-say as the popular science publications seem to be in no mind to dispel this myth.

"The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal, and that the ten miles they have reached could span the distance between the surface of the earth and space."

This part of the article still confuses me though, how does it bring us closer to this?

I came across this while reading up on the topic. It's an interesting paper which, to a layperson like myself, give a plausible theory for how a local variable could in fact account for the results of various QM experiments. I'd be curious how folks who do better understand QM respond to it.

The big problem that I see with this is that we can't control or manipulate any quantum states unless it's a very, very redundant system. As with quantum computing, a calculation has to be run potentially millions of times due to the problem of Heisenberg's uncertainty. Sounds to me like they could probably do this same experiment many times, and get a much better result than 89%, but that's why they're the scientists, not me.

Reading the first couple of comments, it's interesting to note that even if the "transmit information" phrasing in the article was an attempt to dumb things down for a wider audience, it's causing nothing but confusion. This perhaps demonstrates the intelligence of your audience and I would encourage you folks not to take after Wired but stick to your intelligent articles, intelligent audience roots.

Massive douchebag.

I would encourage you to jump off a bridge, how's that for transmitting some information?...

I'm going to put myself into the "disappointed" column as well. I get what you were going after, but the article is quite misleading. Even as a layperson with a cursory interest in the subject I picked up on some things that made me question my understanding of the quantum world. Maybe, if you changed "change" to "measure" it might be better...I don't know. What I do know is that one could easily walk away from this thinking that we'll be able to transmit data via quantum entanglement, which is not the conclusion of the experiment.

@Wudan Master: Are you supposed to be a non-layperson? The way you clump the general public together as boobs in your post is a bit bothersome, especially when you can't spell "per-se" or "become". If you are indeed a non-layperson, then enlighten us as to why we don't know what we're collectively talking about. /frustration

After reading the Ars article and comments, what I _THINK_ they did is now they're able to maintain coherence of entangled particles up to 10 miles, as opposed to a few hundred meters before.

btw, what does "free space" refer to? Some kind of "this many loops around a fiber-optic cable" trick? Or an actual, honest-to-goodness 10 miles of as-the-crow-flies separation between the two particles? Still inside one huge fiber? Or outside of fiber? How was the coherence maintained?

btw, what does "free space" refer to? Some kind of "this many loops around a fiber-optic cable" trick? Or an actual, honest-to-goodness 10 miles of as-the-crow-flies separation between the two particles? Still inside one huge fiber? Or outside of fiber? How was the coherence maintained?

"The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal, and that the ten miles they have reached could span the distance between the surface of the earth and space."

This part of the article still confuses me though, how does it bring us closer to this?

It doesn't, if "traditional signal" means transmission of classical information, which is the only natural thing for it to mean in this context. As the thread makes clear, the confusion is that in the paper they are talking about quantum information, whereas the Ars writeup is muddy on this point (and it's an easy mistake to make). The "traditional signal" for getting some arbitrary quantum state from one place to another without quantum teleportation is to drive it there in a truck (OK, I'm being a bit facetious). In the paper they create the entangled resource, mix it with the state they want to transmit (locally), and then send the other entangled photon through the free-space channel. If we have a satellite that can read the entangled photon as well as create its own we would have the ability to teleport quantum information from Alice to Bob, no matter where they were on Earth. A "traditional signal" (classical information) is just as needed, and it's even drawn in on figure 1a. And even if it weren't, in this scheme we create the entangled photons at the same place and then send one to the destination, which clearly can't violate causality. The main point is that the distances of transmission achieved in this experiment are comparable to what one would need to account for all the atmosphere between Earth and a satellite.

As a side note, since any quantum teleportation scheme requires a classical channel, I'm guessing that the difficult task of setting up and maintaining pre-entangled resources probably isn't worth it. Except maybe for special needs? Like if you really don't want Eve flying in an airplane catching your entangled photons on their way to the satellite.

Edit: I feel I need to back off from one thing I said above. Namely, that this scheme clearly can't violate causality because it distributes the entangled photons from a single local source. This is because one of the entangled photons is mixed with the quantum state to transport after its creation. This makes it a "pre-entangled" resource in a formal sense, so no issues of causality are resolved. (I guess you could say this scheme provides "just-in-time" production of entangled resources, as opposed to entangling a bunch of atoms and transporting half of them in a truck.) The scheme still can't violate causality, just for the usual reason that classical information must be transferred as well.

That said, if the photons take a long time to reach their respective recipients, that clearly puts a bound on how fast the recipient can make use of any quantum information, but it is the same bound as sending classical information anyway. The physical issue of when the photon experiences its mysterious change due to its entangled partner being observed (or whatever) should have no dependence on how far it still has to go until it reaches its recipient. There might not even be a recipient. It's not much of a distinction pragmatically, but it's a big one if we're asking fundamental questions about what quantum teleportation and entanglement mean.

I'm going to put myself into the "disappointed" column as well. I get what you were going after, but the article is quite misleading. Even as a layperson with a cursory interest in the subject I picked up on some things that made me question my understanding of the quantum world. Maybe, if you changed "change" to "measure" it might be better...I don't know. What I do know is that one could easily walk away from this thinking that we'll be able to transmit data via quantum entanglement, which is not the conclusion of the experiment.

@Wudan Master: Are you supposed to be a non-layperson? The way you clump the general public together as boobs in your post is a bit bothersome, especially when you can't spell "per-se" or "become". If you are indeed a non-layperson, then enlighten us as to why we don't know what we're collectively talking about. /frustration

Sorry about my spelling I tend be about 3 words ahead of myself and I have a dodgy keyboard that likes to miss the odd character.

I am as much a layperson as the next man, however I know that this technology is not able to achieve what people think and I've seen enough misguided discussion on the internet to believe that a large number of people think that it will 'someday'

When I read this article I knew a large amount of readers would have their view mistakenly reinforced.

I think that a lot of the reaction stems from a natural defensiveness that people develop because they are so used to seeing science misrepresented on sites like slashdot. I, at least, tend to overreact because it depresses me to read all of the bizarre conclusions that people come to after reading and misunderstanding short articles on complicated topics.

I have to throw in that I think it's the scientists themselves which are misrepresenting the science. The word 'teleport' has a definition, and it's nothing like what is being achieved in these experiments. I understand that it's a complicated topic, but 'teleport' seems to be used because it makes for exciting paper titles rather than because it accurately communicates the ideas in the experiment.

If I understand the article, they sent photons from one location to another and using sophisticated measurements were able to determine that the photons arrived intact, unmolested, and probably unmeasured. The new aspect was the distance involved. But nothing about it resembled 'teleportation'. The media is just the messenger, the misrepresentation is coming from the source.

I object to this line of argument for the simple reason that, were the science to be perfected to the point of making it possible to accomplish the same with macroscopic objects, it would be the functional equivalent of 'teleportation'. To put it another way -- when I deposit my $20 dollar bill into an ATM and later extract it from another ATM across town I don't object that it isn't the 'same' $20 dollar bill.

It strikes me that to object to those speaking in a non-technical, pop-science, environment of 'teleportation' shows both a hypertechnical near-sightedness (failing to see the forest for the trees) as well as simply a lack of imagination and creativity.

Were I to be able to cobble together a source of entangled particles sufficient to compose a macroscopic body and the technical apparatus necessary to scan and transmit the information/measurements from the scan at the target to the source with sufficient fidelity that the entangled particles were effectively arranged to match the source arrangement I think it's fair to say, for (most) intents and purposes, I teleported the thing.

Were I to be able to cobble together a source of entangled particles sufficient to compose a macroscopic body and the technical apparatus necessary to scan and transmit the information/measurements from the scan at the target to the source with sufficient fidelity that the entangled particles were effectively arranged to match the source arrangement I think it's fair to say, for (most) intents and purposes, I teleported the thing.

Unless you've learned how to entangle particles at a distance, which I don't see being done here, you still have to physically move the entangled particles to the destination. You call that 'teleporting'. I call that FedEx. I also don't see any copying going on at all. Not even the copying of the quantum state of a single photon. Creating an entangled pair of photons and getting one half of that pair to fly through the air (the way all photons do) and measuring them isn't copying anything. Nothing here is even a small, itsy bitsy, step towards being able to 'teleport'.

Unless you've learned how to entangle particles at a distance, which I don't see being done here, you still have to physically move the entangled particles to the destination. You call that 'teleporting'. I call that FedEx. I also don't see any copying going on at all. Not even the copying of the quantum state of a single photon. Creating an entangled pair of photons and getting one half of that pair to fly through the air (the way all photons do) and measuring them isn't copying anything. Nothing here is even a small, itsy bitsy, step towards being able to 'teleport'.

Please. The "teleporting" part refers to the quantum state moved from one place to another without needing to go anywhere in between. That entangled particles have to get from point A to point B isn't the part that is fundamentally amazing, and it also isn't what is being called "quantum teleportation." If the name is a bit misleading because people think it is completely analogous to Star Trek, fine, but let's not pretend there isn't a common thread here. It's an evocative, and I think appropriate name for the phenomenon.

And nothing is being copied. In fact, there is a "no-cloning theorem" which shows you can't copy an arbitrary quantum state to arbitrary precision. To move the state from A to B it must be destroyed at A.

Were I to be able to cobble together a source of entangled particles sufficient to compose a macroscopic body and the technical apparatus necessary to scan and transmit the information/measurements from the scan at the target to the source with sufficient fidelity that the entangled particles were effectively arranged to match the source arrangement I think it's fair to say, for (most) intents and purposes, I teleported the thing.

Unless you've learned how to entangle particles at a distance, which I don't see being done here, you still have to physically move the entangled particles to the destination. You call that 'teleporting'. I call that FedEx. I also don't see any copying going on at all. Not even the copying of the quantum state of a single photon. Creating an entangled pair of photons and getting one half of that pair to fly through the air (the way all photons do) and measuring them isn't copying anything. Nothing here is even a small, itsy bitsy, step towards being able to 'teleport'.

What you're 'fedexing' is a non-distinguished set of entangled particles sufficient to create a copy. What presumably would occur as the result of the entanglement, measurement at the source, transport of that information and subsequent measurement at the target is a spontaneous, indistinguishable representation of the source particle(s) at the target.

A better question is whether anything, human or otherwise, living or otherwise, requires the fidelity, the indistinguishability, that quantum teleportation promises for these type of long-haul macroscopic purposes. If I can create a relatively crude copy using other means and get as much out of it, quantum teleportation, even if technically feasible, won't replace the idea of some sort of 'classical' fabber.

If, however, the nature of human identity is tied in some irreducible fashion to the quantum states of the constituent particles, I think quantum teleportation provides the (unrealistic) promise of transporting that identity at or near the speed of light. If that occurs I'll be happy to call it teleportation while you fume that I'm not really 'teleporting' anything.

I think one of the cool ways of looking at it is charting the amount of energy necessary to transport an individual a fixed distance plotted against time. As the time approaches 0 the amount of energy increases asymptotically. At that point there is a discontinuity where, sitting at a point near 0 time and 0 energy is the result of converting ourselves, via quantum teleportation, to a set of measurements and traveling at near the speed of light using (relatively) negligible energy.

So from what every is saying, can I conclude that the only thing they were really able to do was maintain the entanglement over a distance of about 10 miles?

My question is, how would any kind of FTL transmission violate causality? Can someone explain?

It doesn't violate causality because the information is not traveling faster than light. In order for the entanglement to serve a purpose in transport, the measurement and the result of the measurement needs to be transmitted by some other means to the target. This requirement prevents the instantaneous transfer of the quantum state from being used as some sort of means to FTL transmission.

EDIT: I think something else needs to be added here. What would presumably occur with a pair of entangled particles (A/B) is that one particle in the pair, A, would be subsequently entangled with particle C at the source. Then measurement of the A/C pair would cause the state of C to be transferred to B. Without the requirement to pass the measurement and the result of the measurement to the target, FTL transmission would apparently be possible.

No information is transmitted. The end state of the two photons is correlated but random. I'm disappointed that such a basic misunderstanding made its way into an article here. I'll ignore the last sentence as the second half of it was presumably a joke.

Thanks for clearing that up, because I was a bit confused myself. Mechanical engineer on this end.

nkinnan is right-- you may not load a .doc into a photon and have it show up in its entangled friend ten miles away.

Hrmm... so many people mispronounce or misspell this phrase that I would have never guessed it. It does make more sense though. I have to say though, the correct phrasing really doesn't roll off the tongue very well.